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.\" Copyright (c) 2020 Andriy Gapon <avg@FreeBSD.org>
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.Dd November 6, 2021
.Dt PCF8574 4
.Os
.Sh NAME
.Nm pcf8574
.Nd driver for the PCF8574 8-bit I2C IO expander
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device pcf8574"
.Cd "device gpio"
.Cd "device iicbus"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
pcf8574_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides
.Xr gpiobus 4
control over 8 GPIO pins.
The pins are quasi-bidirectional.
Only low output can be actively driven.
High output is equivalent to input.
.Pp
On an
.Xr FDT 4
based system the following properties must be set:
.Bl -tag -width "compatible"
.It Va compatible
Must be set to "nxp,pcf8574".
.It Va reg
The I2C address of
.Nm .
.El
.Pp
The DTS part for a
.Nm
device usually looks like:
.Bd -literal
/ {

	...
	pcf8574@27 {
		compatible = "nxp,pcf8574";
		reg = <0x27>;
	};
};
.Ed
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr gpiobus 4 ,
.Xr iicbus 4
.Sh HISTORY
The
.Nm
driver and this manual page was written by
.An Andriy Gapon Aq Mt avg@FreeBSD.org .
.Sh BUGS
The
.Nm
driver does not support the input change interrupt
that the hardware provides.
